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Reversible Atteunator

System 55 • System 35 • Model 15

Reversible Atteunator

Postby WZOLL » Tue Mar 21, 2017 11:23 pm

Hello. This is my first post and I just wanted to share some info I found. I'm in the progress of building a clone Modular based on the 15 ( there are a few differences like a 901a/bb combo instead of a 921a/bb and a cp3 mixer). When building the CP15 console panel, the schematic was very blurry and broken up and I could not find any info on its function. My original understanding was that when the knob is at the 12 o' clock position the signal passes through. If the the knob was turned counterclockwise, the output signal would be attenuated, and if it was turned clockwise the input signal would be boosted. I was able to piece together a schematic and will attach it to this post. The function of the circuit according to my redrawn schematic is if the knob is at the 12 o' clock position no signal passes through. If the knob is turned counter clockwise, the output signal increases in amplitude from 0 until it reaches the same level as the input signal. This is where things get interesting. If the knob is turned clockwise, the signal is inverted and increases in amplitude from 0 until it reaches the same amplitude as the input signal but flipped. Attached is the schematic. A single board 921 VCO using the original parts and a 911 envelope generator board using the original part are coming soon. Thank you.
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